(a) Technical Field
The present invention relates to a driving force control method during engine clutch slipping in a transmission mounted electric device (TMED) HEV in which a motor and a transmission are connected. More particularly, the present invention relates to an enhanced driving force control method in case of an engine clutch slipping in TMED hybrid electric vehicle (HEV), which allows a separator motor (HSG) to bear a load while performing a low-speed and large-torque operation in a zone where noise, vibration and harshness (NVH) is disadvantageous when a vehicle starts to improve engine operation to be maintained in a zone where the NVH is advantageous.
(b) Background Art
Due to the demand for improving fuel efficiency of a vehicle and the demand for saving fuel while meeting a discharge gas regulation of various countries, development of a hybrid electric vehicle (HEV) using both an engine and an electric motor as power has been developed. The hybrid electric vehicle is a type of vehicle that uses both the engine and the electric motor as driving force of the vehicle and as a result, the engine is driven when the vehicle is driven at a high speed and both the engine and the electric motor are driven when the driving force requires an increase, whereas the electric motor is driven when the vehicle is driven in the city (e.g., with high congestion).
The hybrid electric vehicle is driven by two power sources, the engine and the motor, and an engine clutch is disposed between the power sources and as a result, the hybrid electric vehicle operates in an electric vehicle (EV) mode or HEV mode based on a connection (coupling) of the engine clutch and during this process, optimal output torque may be provided by considering how the engine and the motor harmoniously operate.
The engine outputs clutch torque and additional torque for maintaining a speed when the engine clutch slips (see FIG. 1) and a control for the engine and the motor to maintain a predetermined speed is executed during learning engine clutch transmission torque, and as a result, the torque of the engine needs to be increased as much as the clutch torque when pressure is applied (see FIG. 2). In FIGS. 1 and 2, We represents an engine angular speed and Wm represents a motor angular speed. It can be seen that the engine is operated in a zone in which NVH is disadvantageous in a torque zone where engine torque Te is substantially large based on clutch slipping transmission torque T_clutch of a substantially large torque zone in both a behavior when the engine clutch slip-starts and a behavior when the engine clutch transmission torque is learned.
In general, an operation speed of the engine is adjusted to approximately an idle revolutions per minute (rpm) when the vehicle starts and the engine is required to output additional torque to maintain the clutch torque and the engine speed when the engine clutch slips. Since the engine bears an engine clutch torque load, the engine operates with a low speed and large torque as schematically illustrated in FIG. 3. As a result, the engine operates in an operation zone in which noise, vibration, and harshness (NVH) is disadvantageous.
In this regard, the present applicant has disclosed a system and a method for learning the transmission torque of the engine clutch of the hybrid electric vehicle, which maintain the engine at a predetermined speed (e.g., idle speed) and allow a start generator to appropriately bear the transmission torque of the engine clutch based on operation hydraulic pressure of the engine clutch to prevent engine booming in the low-speed and large-torque zone at the time of learning the transmission torque and enhance the NVH, while learning the transmission torque of the engine clutch of the hybrid electric vehicle.
Additionally, a shift control device of the related art includes a motor assist control part that generates assist torque equivalent to a deviation between required torque for an internal combustion engine and output torque of the internal combustion engine during shifting a driving device that includes a generator used to assist the internal combustion engine in a motor to correct assist torque using correction torque when clutch slipping occurs, in a HEV including the internal combustion engine and the motor.
Another developed related art teaches a hybrid electric vehicle having a motor and an engine selectively connected on a drive line by a controller configured to provide additional motor torque to compensate for engine inertia resistance based on a clutch slipping speed value during a period of clutch engagement and a clutch pressure value and the engine is connected to a starter used to start the engine when additional torque is required.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.